Viruses induce disease in the central nervous system (CNS) by either killing or disrupting essential functions of neurons within the brain and spinal cord. We propose to use well characterized models of virus-induced CNS disease to investigate the mechanisms by which viruses cause neuronal cell death and injury to the brain and spinal cord. We will delineate the specific cell signaling pathways involved in virus-induced death and tissue injury within the CNS and evaluate these signaling pathways as therapeutic targets for virus-induced CNS disease. Our experiments are expected to lead to the identification of novel therapeutic targets for virus- induced CNS disease. Apoptosis is an established mechanism of virus-induced cell death during viral encephalitis and occurs in the brain following experimental infection with a wide variety of viruses. Apoptosis is also emerging as a mechanism of motor neuron cell death in virus-induced myelitis in humans. Inhibition of caspase 3, the executioner caspase of apoptotic cell death, results in decreased severity of virus-induced encephalitis. In specific aim 1 we will test the hypothesis that inhibition of the signaling pathways that lead to apoptotic cell death wil prevent neuronal death and provide novel targets for virus induced brain and spinal cord disease following infection with a variety of clinically relevant viruses. Reovirus infection of neonatal mice provides a well characterized model system for understanding viral pathogenesis within both the brain and spinal cord. We have already identified that the extrinsic and intrinsic apoptotic pathways and JNK signaling are activated in the brain following reovirus infection and contribute to reovirus-induced neuronal apoptosis. We propose to identify whether these pathways are also activated: (i) in our recently developed model of reovirus-induced myelitis: (ii) in the brains of mice infected with West Nile Virus (WNV) and herpes simplex virus (HSV): (iii) following virus (reovirus, WNV, HSV) infection of ex vivo brain slice cultures and: (iv) in human tissue from patients with virus-induced CNS disease, and to characterize their role in viral pathogenesis. Virus infection of the CNS results in activation of innate immune responses, including the up-regulation of interferon (IFN) and increased expression of IFN stimulated genes (ISG). ISG influence apoptosis, although the mechanism by which this occurs and the role of these genes in viral pathogenesis remains unknown. In specific aim 2 we will investigate the role of specific ISG, with putative apoptotic functions, in virus (reovirus, WNV, HSV)-induced pathogenesis within the mouse brain and spinal cord, following viral infection of ex vivo brain slice cultures and in tissue from patients with virus-induced CNS disease. Gliosis (activation of microglia and astrocytes) is a hallmark of neuroinflammation. Gliosis has been demonstrated in vitro and in vivo following infection with Japanese encephalitis virus (JEV) and inflammatory mediators associated with gliosis have been detected in the brain during viral encephalitis. However, the role of gliosis in acute virus-induced CNS disease remains incompletely understood, particularly within the spinal cord. Although gliosis may play a role in inhibiting virl replication by facilitating the removal of infected cells it has been proposed that this protective role may be overshadowed by the release of several factors from activated glia that induce neurodegeneration and severe injury to bystander cells. In specific aim 3 we hypothesize that gliosis contributes to pathogenesis following viral infections of the CNS. We will test this hypothesis by investigating the role gliosis in virus (reovirus, WNV, HSV)-induced pathogenesis within the mouse brain and spinal cord, following viral infection of ex vivo brain slice cultures and in tissue from patients with virus-induced CNS disease.